PERFORMANCE PREDICTIONS OF ALTERNATIVE, LOW-COST ABSORBENTS FOR OPEN-CYCLE ABSORPTION SOLAR COOLING

To achieve solar fractions greater than 0.90 using the open-cycle absorption refrigeration system, considerable sorbent solution storage is necessary. Sorbent solutions currently under consideration, such as aqueous solutions of lithium chloride and lithium bromide, may be too costly to exploit the open-cycle storage concept. Having identified the absorber as the system component whose performance is affected the most by a change in absorbent, an absorber model was selected from available literature pertaining to simultaneous heat and mass transfer. Low cost absorbent candidates were selected and their physical properties were either located in the literature, measured, or estimated. Absorber operating parameters were selected and the model was then used to estimate absorber performance for each absorbent in terms of cooling capacity per unit of absorber area. After specifying system parameters such as absorber capacity and cooling load, the absorber area, absorbent cost; and sorbent solution pumping power and storage volume were estimated for each candidate. The most promising of the absorbents considered was a mixture of two parts lithium chloride and one part zinc chloride. The estimated capacities per unit absorber area were 50-70% less than those of lithium bromide; however, the lithium bromide cost for a system sized to cool a 190 m(2) residential structure was estimated to be eight times that for the lithium-zinc chloride mixture. Both the lithium-zinc chloride mixture and lithium bromide solutions had estimated pumping powers of less than 0.1 kW. The solubility of the lithium-zinc chloride mixture at absorber conditions was improved over that of lithium bromide, reducing the risk of solidification of the solution.